Antiplasmodial Compounds from Deep-Water Marine Invertebrates

Novel drug leads for malaria therapy are urgently needed because of the widespread emergence of resistance to all available drugs. Screening of the Harbor Branch enriched fraction library against the Plasmodium falciparum chloroquine-resistant strain (Dd2) followed by bioassay-guided fractionation led to the identification of two potent antiplasmodials; a novel diterpene designated as bebrycin A (1) and the known C21 degraded terpene nitenin (2). A SYBR Green I assay was used to establish a Dd2 EC₅₀ of 1.08 ± 0.21 and 0.29 ± 0.02 µM for bebrycin A and nitenin, respectively. Further analysis was then performed to assess the stage specificity of the inhibitors antiplasmodial effects on the Dd2 intraerythrocytic life cycle. Exposure to bebrycin A was found to block parasite maturation at the schizont stage if added any time prior to late schizogony at 42 hours post invasion, (HPI). In contrast, early life cycle exposure to nitenin (prior to 18 HPI) was identified as crucial to parasite inhibition, suggesting nitenin may target the maturation of the parasite during the transition from ring to early trophozoite (6–18 HPI), a novel property among known antimalarials.

Terpenes from Eunicea Laciniata and Plexaurella Nutans

A new 7,8–epoxydolabella–3(E)–12(18)–diene (1), diterpenoid together with three known compounds were isolated from a Honduras gorgonian Eunicea laciniata. The relative stereochemistry of 1 was established by spectroscopic studies and the antiprotozoal and antimicrobial activities of dolabellane diterpenoids 2–4 are reported. Three known cadinane type sesquiterpenes were also isolated from Honduras gorgonian Plexaurella nutans.

Rosiglitazone is superior to resveratrol in inducing the expression of glyceroneogenic genes in adipose tissue from obese participants

We compared the effects of resveratrol and rosiglitazone, alone and in combination, on indices of fatty acid re-esterification in cultured adipose tissue from obese participants (n = 17) undergoing gastric bypass. Rosiglitazone induced PDK4 and PEPCK gene expression to a greater extent than resveratrol. Co-treatment with both compounds induced PDK4 and PEPCK expression in parallel with reductions in the fatty acid to glycerol ratio. Our findings suggest beneficial effects of resveratrol and rosiglitazone co-treatment.

Analogues of the Potent Antitumor Compound Leiodermatolide from a Deep-Water Sponge of the Genus Leiodermatium

Two new analogues of the potent antitumor compound leiodermatolide, which we call leiodermatolides B and C, have been isolated from specimens of a deep-water sponge of the genus Leiodermatium collected off Florida. The compounds were purified using standard chromatographic methods, and the structures defined through interpretation of the HRMS and 1D and 2D NMR data. Leiodermatolide B (2) lacks the C-21 hydroxy group found in leiodermatolide and has equal potency as the parent compound, providing a simpler analogue for possible clinical development. It inhibits the proliferation of the AsPC-1 human pancreatic adenocarcinoma cell line with an IC₅₀ of 43 nM. Leiodermatolide C (3) has a modified macrolide ring and is over 85-fold less potent with an IC₅₀ of 3.7 μM against the same cell line. These compounds add to the knowledge of the pharmacophore of this class of potent antitumor agents.

Deepwater marine litter densities and composition from submersible video-transects around the ABC-islands, Dutch Caribbean

Baseline data on anthropogenic seafloor debris contamination in the year 2000 is provided for 24 submersible video transects at depths of 80-900 m, off the Dutch ABC-islands (Aruba, Bonaire, Curaçao), in the southeastern Caribbean Sea. In total, 202 objects were documented from a combined 21,184 m of transect, ranging from sandy lower island-slope to rocky upper island-slope habitat. Debris densities differed significantly with depth. Highest debris accumulation (0.459 items 100 m(-2) or 4590 items per km(2)) occurred at depths of 300-600 m on more shallow-sloping (20-30°) sand and silt bottoms. The overall average debris density was 0.27 objects per 100 m(2) (or 2700 items per km(2)), which is an order of magnitude higher than most other deepwater debris studies. What we describe may be representative for other small, populated, steep volcanic Caribbean islands. Food and beverage-related items were the single largest usage category identified (44% of objects; mostly glass beverage bottles).

The bacterial community of the lithistid sponge Discodermia spp. as determined by cultivation and culture-independent methods

The marine lithistid sponge Discodermia spp. (Family Theonellidae) contains many types of associated bacteria visible in the mesohyl while biofilms cover the pinacoderm. This study determined the identity of bacteria associated with members of the genus Discodermia using microbial culture, 16S rRNA gene clone libraries and fluorescence in situ hybridization. Four samples of Discodermia spp. were collected at depths between 24-161 m near Grand Bahama Island and Cay Sal Bank, Bahamas. A total of 80 unique isolates and 94 different clone sequences from at least eight bacterial classes were obtained. It appeared that Discodermia spp. may have a core community of bacteria that is common to all sponges of this genus. Species of at least six different classes of bacteria were regularly found in most of the sponge specimens collected, irrespective of collection depth or location. This indicates that a diverse spectrum of bacteria is associated with lithistid sponges irrespective of the transient seawater community that enters the sponge.

Leiodermatolide, a potent antimitotic macrolide from the marine sponge Leiodermatium sp

Leiodermatolide is a structurally unique macrolide, isolated from the deep-water marine sponge Leiodermatium sp ., which exhibits potent antiproliferative activity against a range of human cancer cell lines (IC50 <10 nM) and dramatic effects on spindle formation in mitotic cells. Its unprecedented polyketide skeleton and stereochemistry were established using a combination of experimental and computational (DP4) NMR methods, and molecular modelling.

Gymnochromes E and F, cytotoxic phenanthroperylenequinones from a deep-water crinoid, Holopus rangii

Bioactivity-guided fractionation of metabolites from the crinoid Holopus rangii led to the discovery of two new phenanthroperylenequinone derivatives, gymnochromes E (1) and F (2). Gymnochrome E showed cytotoxic activity toward the NCI/ADR-Res with an IC(50) of 3.5 microM. It also inhibited histone deacetylase-1 with an IC(50) of 3.3 microM. Gymnochrome F was a moderate inhibitor of myeloid cell leukemia sequence 1 (MCL-1) binding to Bak. Two anthraquinone metabolites, emodic acid (4) and its new bromo derivative (5), were also isolated from the crinoid and show remarkable similarity to the phenanthroperylenequinone core, suggesting that these metabolites share the same polyketide biosynthetic pathway.

Isolation, synthesis, and biological activity of aphrocallistin, an adenine-substituted bromotyramine metabolite from the Hexactinellida sponge Aphrocallistes beatrix

A new adenine-substituted bromotyrosine-derived metabolite designated as aphrocallistin (1) has been isolated from the deep-water Hexactinellida sponge Aphrocallistes beatrix. Its structure was elucidated on the basis of spectral data and confirmed through a convergent, modular total synthetic route that is amenable toward future analogue preparation. Aphrocallistin inhibits the growth of a panel of human tumor cell lines with IC(50) values ranging from 7.5 to >100 microM and has been shown to induce G1 cell cycle arrest in the PANC-1 pancreatic carcinoma cell line. Aphrocallistin has been fully characterized in the NCI cancer cell line panel and has undergone in vitro ADME pharmacological profiling.

Neopeltolide, a macrolide from a lithistid sponge of the family Neopeltidae

A new marine-derived macrolide designated as neopeltolide (1) has been isolated from a deep-water sponge of the family Neopeltidae. Its structure was elucidated on the basis of spectroscopic data interpretation. Neopeltolide (1) is a potent inhibitor of the in vitro proliferation of the A-549 human lung adenocarcinoma, the NCI-ADR-RES human ovarian sarcoma, and the P388 murine leukemia cell lines, with IC50's of 1.2, 5.1, and 0.56 nM, respectively. Neopeltolide (1) also inhibited the growth of the fungal pathogen Candida albicans with a minimum inhibitory concentration of 0.62 microg/mL.

Two new cytotoxic linderazulenes from a deep-sea gorgonian of the genus Paramuricea

The known compound linderazulene (1) and two new linderazulenes (2, 3) were isolated from a deep-sea gorgonian Paramuricea sp. The structures of 2 and 3 were determined through spectroscopic methods. Compounds 1-3 show moderate in vitro cytotoxicity against the P388 murine leukemia cell line with IC(50)'s of 18.8, 2.7, and 15.6 microg/mL, respectively. Compound 2 showed moderate activity against the PANC-1 pancreatic cell line with an IC(50) of 18.7 microg/mL.

Plakolide A, a new gamma-lactone from the marine sponge Plakortis sp

Plakolide A (1), a new alpha-exomethylene-gamma-lactone isolated from the marine sponge Plakortis sp., was found to inhibit inducible nitric oxide synthase (iNOS) activity. The isolation, structure elucidation, and biological activity of plakolide A is described.

Characterization of genetic markers for in vitro cell line identification of the marine sponge Axinella corrugata

The marine sponge Axinella corrugata is being developed as a model organism for in vitro marine invertebrate research. Molecular genetics methods such as DNA fingerprinting [amplified fragment length polymorphism (AFLP) and single-stranded conformation polymorphism (SSCP)] and single-locus DNA sequence analyses were applied to this model to meet the primary objective of identifying positive A. corrugata-specific molecular markers that will aid in verifying cell identity in vitro and distinguish sponge cells from potential microbial contaminants. The extent of intra- and interspecific variation in these markers from geographically distinct samples of A. corrugata and closely related sponge taxa was also assessed. Two novel nuclear loci along with intervening transcribed spacer (ITS) regions of nuclear rRNA were characterized, although the latter appeared to better meet primary marker criteria, such as taxonomic specificity and high frequency of detection (via polymerase chain reaction [PCR]) from different individuals (n > 40) and cell cultures. Phylogenetic and phylogeographic analyses of ITS DNA sequences helped clarify taxonomies and also suggested species boundaries between and among western Atlantic and eastern Atlantic/Indian Ocean A. corrugata and Axinellidae samples. Patterns of genetic variation have important implications for the systematics, evolution, and chemical ecology of A. corrugata and related axinellids and are discussed.

The synthesis of cyclonucleotides with fixed glycosidic bond linkages as putative agonists for P2-purinergic receptors

Cyclonucleotides with fixed glycosidic bond linkages were investigated as possible ligands for purinoceptors in PC12 cells. P2Y2-purinoceptors were not activated by the ATP analogue, 8,2'-thioanhydroadenosine-5'-triphosphate (4) and only weakly by the UTP analogue, 2,2' -anhydrouridine-5'-triphosphate (6). However, both analogues were agonists for P2X2-purinoceptors although the potencies were approximately 30-fold less than that of the parent nucleotides.

Trophic effects of purines in neurons and glial cells

In addition to their well known roles within cells, purine nucleotides such as adenosine 5' triphosphate (ATP) and guanosine 5' triphosphate (GTP), nucleosides such as adenosine and guanosine and bases, such as adenine and guanine and their metabolic products xanthine and hypoxanthine are released into the extracellular space where they act as intercellular signaling molecules. In the nervous system they mediate both immediate effects, such as neurotransmission, and trophic effects which induce changes in cell metabolism, structure and function and therefore have a longer time course. Some trophic effects of purines are mediated via purinergic cell surface receptors, whereas others require uptake of purines by the target cells. Purine nucleosides and nucleotides, especially guanosine, ATP and GTP stimulate incorporation of [3H]thymidine into DNA of astrocytes and microglia and concomitant mitosis in vitro. High concentrations of adenosine also induce apoptosis, through both activation of cell-surface A3 receptors and through a mechanism requiring uptake into the cells. Extracellular purines also stimulate the synthesis and release of protein trophic factors by astrocytes, including bFGF (basic fibroblast growth factor), nerve growth factor (NGF), neurotrophin-3, ciliary neurotrophic factor and S-100beta protein. In vivo infusion into brain of adenosine analogs stimulates reactive gliosis. Purine nucleosides and nucleotides also stimulate the differentiation and process outgrowth from various neurons including primary cultures of hippocampal neurons and pheochromocytoma cells. A tonic release of ATP from neurons, its hydrolysis by ecto-nucleotidases and subsequent re-uptake by axons appears crucial for normal axonal growth. Guanosine and GTP, through apparently different mechanisms, are also potent stimulators of axonal growth in vitro. In vivo the extracellular concentration of purines depends on a balance between the release of purines from cells and their re-uptake and extracellular metabolism. Purine nucleosides and nucleotides are released from neurons by exocytosis and from both neurons and glia by non-exocytotic mechanisms. Nucleosides are principally released through the equilibratory nucleoside transmembrane transporters whereas nucleotides may be transported through the ATP binding cassette family of proteins, including the multidrug resistance protein. The extracellular purine nucleotides are rapidly metabolized by ectonucleotidases. Adenosine is deaminated by adenosine deaminase (ADA) and guanosine is converted to guanine and deaminated by guanase. Nucleosides are also removed from the extracellular space into neurons and glia by transporter systems. Large quantities of purines, particularly guanosine and, to a lesser extent adenosine, are released extracellularly following ischemia or trauma. Thus purines are likely to exert trophic effects in vivo following trauma. The extracellular purine nucleotide GTP enhances the tonic release of adenine nucleotides, whereas the nucleoside guanosine stimulates tonic release of adenosine and its metabolic products. The trophic effects of guanosine and GTP may depend on this process. Guanosine is likely to be an important trophic effector in vivo because high concentrations remain extracellularly for up to a week after focal brain injury. Purine derivatives are now in clinical trials in humans as memory-enhancing agents in Alzheimer's disease. Two of these, propentofylline and AIT-082, are trophic effectors in animals, increasing production of neurotrophic factors in brain and spinal cord. Likely more clinical uses for purine derivatives will be found; purines interact at the level of signal-transduction pathways with other transmitters, for example, glutamate. They can beneficially modify the actions of these other transmitters.

Purine and pyrimidine nucleotides activate distinct signalling pathways in PC12 cells

The role of extracellular nucleotides in intracellular signalling and neurosecretion was assessed in PC12 cells. Activation of phospholipase C and increased [Ca2+]i were mediated by purinoceptors with an agonist potency profile, ATP approximately UTP > 2-methylthioadenosine triphosphate (2-MeSATP), typical of P2U. ATP also evoked a rapid acidification followed by a more gradual alkalinization (measured with 2',7'-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF)), while UTP induced only a gradual alkalinization. The amiloride analogue 5-(N-ethyl-N-isopropyl)amiloride (EIPA) attenuated the alkalinization phase suggesting activation of the Na+/H+ exchanger by ATP and UTP. Using bisoxonol and [3H]tetraphenylphosphonium ([3H]TPP+) as potential-sensitive probes, we showed that while ATP rapidly depolarized PC12 cells in an Na(+)-dependent manner, UTP evoked a much reduced and delayed response. The potency profile (ATP approximately 2-MeSATP approximately adenosine 5'-O-(3-thiotriphosphate) (ATP gamma S) >> UTP, alpha, beta-methyleneATP) suggested involvement of a receptor subtype distinct from P2U. Secretion of endogenous dopamine was also assessed. Those nucleotides that induced depolarization (ATP, 2-MeSATP, ATP gamma S) were also the most potent secretagogues. UTP was ineffective. Our results suggest that ATP stimulates distinct purinoceptor subtypes and induces neurosecretion through the activation of multiple signalling pathways.

Analogues of the marine immunosuppressant microcolin A: preparation and biological activity

A series of analogs of the immunosuppressive lipopeptide microcolin A has been prepared and evaluated for in vitro activity in the human and murine two-way mixed lymphocyte reaction. The compounds tested were obtained by semisynthetic modification and chemical degradation of the natural product. The relative potencies of these analogs suggest that the hydroxyproline and 5-methyl-3-pyrrolin-2-one portion of the molecule are important for immunosuppressive activity and that other structural elements may play an ancillary role. Methanolysis of microcolin A also led to a novel immunosuppressive lactone analog.

mtDNA sequences suggest a recent evolutionary divergence for Beringian and northern North American populations

Conventional descriptions of the pattern and process of human entry into the New World from Asia are incomplete and controversial. In order to gain an evolutionary insight into this process, we have sequenced the control region of mtDNA in samples of contemporary tribal populations of eastern Siberia, Alaska, and Greenland and have compared them with those of Amerind speakers of the Pacific Northwest and with those of the Altai of central Siberia. Specifically, we have analyzed sequence diversity in 33 mitochondrial lineages identified in 90 individuals belonging to five Circumpolar populations of Beringia, North America, and Greenland: Chukchi from Siberia, Inupiaq Eskimos and Athapaskans from Alaska, Eskimos from West Greenland, and Haida from Canada. Hereafter, we refer to these five populations as "Circumarctic peoples." These data were then compared with the sequence diversity in 47 mitochondrial lineages identified in a sample of 145 individuals from three Amerind-speaking tribes (Bella Coola, Nuu-Chah-Nulth, and Yakima) of the Pacific Northwest, plus 16 mitochondrial lineages identified in a sample of 17 Altai from central Siberia. Sequence diversity within and among Circumarctic populations is considerably less than the sequence diversity observed within and among the three Amerind tribes. The similarity of sequences found among the geographically dispersed Circumarctic groups, plus the small values of mean pairwise sequence differences within Circumarctic populations, suggest a recent and rapid evolutionary radiation of these populations. In addition, Circumarctic populations lack the 9-bp deletion which has been used to trace various migrations out of Asia, while populations of southeastern Siberia possess this deletion. On the basis of these observations, while the evolutionary affinities of Native Americans extend west to the Circumarctic populations of eastern Siberia, they do not include the Altai of central Siberia.

Intracellular signalling by nucleotide receptors in PC12 pheochromocytoma cells

The effect of extracellular ATP was studied in PC12 cells, a neurosecretory line that releases ATP. The addition of micromolar concentrations of ATP to PC12 cells evoked a transient increase in the cytosolic free Ca2+ concentration ([Ca2+]i), as measured with the Ca(2+)-sensitive dye fura 2. AMP and adenosine were without effect, ruling out the involvement of P1 receptors in mediating this response. The increase in [Ca2+]i was reduced in calcium-free media and virtually eliminated by the addition of EGTA, suggesting that calcium influx was the primary response initiated by extracellular ATP. Nucleotide triphosphates such as UTP and, to a lesser degree, ITP also evoked an increase in [Ca2+]i while GTP and CTP had little effect. In order to identify the receptor subtype mediating this response, the efficacy of ATP and ATP cogeners was assessed. The rank order potency was ATP > adenosine 5'-[gamma-thio]triphosphate > ADP > 2-methylthioadenosine triphosphate (2-MeSATP) approximately adenosine 5'-[beta-thio]diphosphate >> adenosine 5'-[alpha beta-methylene] triphosphate, adenosine 5'[beta gamma-imido]triphosphate. This profile is not characteristic of either the P2X or the conventional P2Y receptors. The Ca2+ response exhibited desensitization to ATP that was dependent on the extracellular metabolism of ATP. UTP was equally effective in desensitizing the response. ATP, UTP, ITP, and to a much lesser extent 2MeSATP increased inositol phosphate production in a dose-dependent manner, suggesting receptor coupling to phosphatidylinositol-specific phospholipase C. These data are consistent with the view that PC12 cells express a class of non-P2Y nucleotide receptors (P2N) that mediate calcium influx and the accumulation of inositol phosphates.

Absence of the Asian-specific region V mitochondrial marker in Native Beringians

The Asian-specific 9-bp deletion between the genes for mitochondrial cytochrome oxidase II and lysine transfer RNA has been used to trace aboriginal human movements out of Southeast Asia and into portions of the South Pacific. Although it has been used to estimate the number of independent lineages that occur in the New World, it has not been studied in native peoples of the Beringian region. Thus, we have used PCR to amplify and compare the lengths of DNA segments surrounding this deletion in native peoples of Beringia and the adjacent regions, as well as natives of the Altai Mountains of Southwestern Siberia. Of the 176 individuals analyzed here, the deletion was found in only 3 of 25 individuals from the Ust-Kan region of the Altai Mountains. We comment on the distribution of this marker and on potential relationships between Beringians and other Native American groups in which this marker has been surveyed. One Chukchi possessed three copies of the 9-bp sequence, which suggests (1) that the number of copies of this sequence in humans may be more variable than had been believed and (2) that a mechanism of replication based on tandem duplication may be a potential explanation for the origin of this length mutation in humans.

Simultaneous isolation of total cellular RNA and DNA from tissue culture cells using phenol and lithium chloride

A rapid procedure for the isolation of intact total cellular RNA from cultured cells is described. This method combines the simultaneous disruption of cells and extraction of nucleic acids in a single step with the use of phenol and a buffer containing 100 mM LiCl. Total cellular RNA can be isolated in approximately 2 hours. The yield and quality of the RNA is comparable to the more widely employed methods requiring extensive preparatory steps such as extraction using guanidinium thiocyanate and subsequent CsCl gradient centrifugation. The RNA isolated using our procedure contains transcripts up to 10 kb in length and is suitable for Northern analysis. This procedure also yields high-molecular-weight DNA, which is a suitable substrate for restriction endonucleases.

Fluorescent molecular rotors: a new class of probes for tubulin structure and assembly

9-(Dicyanovinyl)julolidine (DCVJ) is a fluorescent dye whose intramolecular rotational relaxation is solvent dependent. Since its quantum yield increases with decreasing free volume, this molecule has been very useful in monitoring synthetic polymer reactions and measuring local microviscosity changes in phospholipid bilayers [Loutfy, R. O. (1986) Pure Appl. Chem. 58, 1239-1248; Kung, C. E., & Reed, J. K. (1986) Biochemistry 25, 6114-6121]. We have used DCVJ to follow the polymerization of tubulin, a protein that can assemble into a variety of polymorphic microstructures. DCVJ binding to free tubulin is accompanied by an increase in quantum yield, indicating that DCVJ has become partially immobilized. At 4 degrees C, DCVJ binds to a single population of high-affinity hydrophobic sites (Kd = 1.12 +/- 0.26 microM) with a stoichiometry that is protein concentration dependent. n, the number of moles of DCVJ bound per mole of alpha beta dimer, approaches 1 at concentrations less than or equal to 0.5 mg/mL but decreases to a lower limit of approximately 0.3 at concentrations greater than or equal to 2.0 mg/mL. The quantum yield also increases with increasing protein concentration. This trend is unaltered by the presence of microtubule-associated proteins. These results are analyzed in terms of a concentration-dependent oligomerization of tubulin at 4 degrees C. When tubulin is polymerized at 37 degrees C to microtubules or to sheets in the presence of Zn2+, the fluorescence intensity of DCVJ increases although the magnitude of this increase differs significantly. We are able to use the distinct fluorescent and binding characteristics of the bound dye to distinguish between these two polymorphs on a molecular level.

The effect of nerve growth factor on the development of sodium channels in PC12 cells

We have studied the development of the action potential Na+ channels in PC12 cells, an established line that has been useful as a model for neuronal differentiation. In continuous culture PC12 cells, although electrically inexcitable, nevertheless have a low level of Na+ channels as judged by the increase in 22Na+ uptake in the presence of veratridine and scorpion toxin. These two neurotoxins have been shown to promote activation of Na+ channels in a variety of electrically excitable cells. Following treatment with nerve growth factor (NGF), conditions which induce differentiation to an electrically excitably neuronal-cell type, the neurotoxin-activated 22Na+ uptake increases approximately 12-fold, on a per cell basis, reaching a maximum in 12-16 days. The dose-response curves for veratridine and scorpion toxin are unchanged by NGF treatment (K0.5 for veratridine, 18-14 microM; K0.5 for scorpion toxin, 120-96 nM). Na+ channels in both undifferentiated and differentiated cells are tetrodotoxin sensitive and NGF treatment has no effect on the inhibition constant (Ki, 10-12 nM). Na+ channel sites were measured directly by the specific binding of [3H]saxitoxin. In NGF-treated cells, the saxitoxin receptor density reaches 154 fmol/mg protein (Kd, 1.3 nM), a level comparable to other excitable cells. Levels in control cells were too low to measure accurately. These findings show that NGF treatment of PC12 cells leads to a substantial increase in the expression of neurotoxin-sensitive Na+ channels. Furthermore, these channels are pharmacologically similar, if not identical, to those which exist in undifferentiated cells and therefore do not appear to result from the conversion of preexisting channels.

Traumatic mesenteric arteriovenous fistula presenting as the superior mesenteric artery syndrome

Arteriovenous fistulas of the mesentery are rare sequelae of abdominal injuries or operations. Symptoms, when present, are most often due to intestinal ischemia or portal hypertension. Cardiac failure is less common, and the case described in this report is, to our knowledge, the first in which the patient presented with duodenal obstruction--the superior mesenteric artery syndrome. A bruit is an expected finding and a thrill is pathognomonic of an arteriovenous fistula. With rare exception, operation is indicated to dismantle the fistula.

Modification of the tetrodotoxin receptor in Electrophorus electricus by phospholipase A2

The effects of phospholipase A2 treatment on the tetrodotoxin receptors in Electrophorus electricus was studied. (1) The binding of [3H]tetrodotoxin to electroplaque membranes was substantially reduced by treatment of the membranes with low concentrations of phospholipase A2 from a number of sources, including bee venom, Vipera russelli and Crotalus adamanteus and by beta-bungarotoxin. (2) Phospholipase A2 from bee venom and from C. adamanteus both caused extensive hydrolysis of electroplaque membrane phospholipids although the substrate specificity differed. Analysis of the phospholipid classes hydrolyzed revealed a striking correlation between loss of toxin binding and hydrolysis of phosphatidylethanolamine but not of phosphatidylserine. (3) The loss of toxin binding could be partially reversed by treatment of the membranes with bovine serum albumin, conditions which are known to remove hydrolysis products from the membrane. (4) Equilibrium binding studies on the effects of phospholipase A2 treatment of [3H]tetrodotoxin binding showed that the reduction reflected loss of binding sites and not a change in affinity. (5) These results are interpreted in terms of multiple equilibrium states of the tetrodotoxin-receptors with conformations determined by the phospholipid environment.

Interaction of nonylguanidine with the sodium channel

Alkyl and aromatic guanidines interact strongly with the tetrodotoxin (TTX)- receptor site in eel electroplaque membranes, showing competition with TTX. That these guanidines could be useful as highly reversible small molecular weight blockers of Na+ currents is therefore suggested. We have investigated the mechanisms of interaction of one of these derivatives, nonylguanidine, by studying its effects on Na+ currents in squid giant axons using voltage clamp techniques. Although nonylguanidine competed with TTX for binding to eel electroplaque membrane fragments (Ki = 1.8 X 10(-5) M), it reversibly blocked both inward and outward Na+ currents in intact axons only if applied to the interior. In axons with the Na+ inactivation removed by papain nonylguanidine produced a time-dependent block very similar to that reported for strychnine and pancuronium. The reduction of steady-state currents in these axons was also voltage-dependent, with increasing block observed with increasing step depolarization. These results suggest that nonylguanidine binds to a site accessible from the axoplasmic side of the channel, simulating Na+ inactivation in papain-treated axons and competing with the normal inactivation process in untreated axons. The competition between internal nonylguanidine and external TTX may result from perturbation by the positively charged nonylguanidine of the TTX-binding site from within the channel itself.

Split thickness skin grafting of the plantar surface of the foot after wide excision of neoplasms of the skin

Results of our studies show split thickness skin grafts are an effective cover for plantar surface defects resulting from tumor excision. Long term follow-up studies of these patients revealed no graft failures. The ease with which split thickness skin grafts can be performed makes it the treatment of choice for reconstruction of areas of excison of neoplasms of the skin on the plantar surface of the foot.

Properties of the tetrodotoxin binding component in plasma membranes isolated from Electrophorus electricus

The biochemical properties of the electrically excitable sodium channels in the electroplaque of Electrophorus electricus were investigated using tritiated tetrodotoxin (TTX) as a specific membrane probe. Membrane fragments from the electroplaque were isolated essentially by differential centrifugation and characterized with respect to the plasma membrane markers acetylcholine receptors, acetylcholinesterase, (Na+ + K+)ATPase, and [3H]TTX binding. Equilibrium binding studies showed that [3H]TTX bound to a single population of noninteracting receptor sites with an apparent dissociation constant of 6 +/- 1 X 10(-9) M. The toxin-membrane complex dissociated with a first-order rate constant of 0.012 sec-1. Studies on the pH dependence of complex formation demonstrated the requirement for an ionizable, functional group with a pK of 5.3 and this group has been shown to be a carboxyl. Treatment of the membranes with trimethyloxonium tetrafluoroborate, a carboxyl group modifying reagent, resulted in an irreversible loss in the binding of [3H]TTX, which could be prevented by low concentrations of TTX or saxitoxin. This decrease was due to a reduction in the total number of binding sites and not to a decrease in toxin binding affinities. The relative binding affinities of various monovalent alkali metal and polyatomic cations for the TTX-receptor site showed that this site displayed cation discrimination properties which were similar to those reported previously for the electrically excitable sodium channel in intact nerve fibers. A possible role for this site in the ion selectivity of the sodium channel is proposed.